1. Field of the Invention
The present embodiments relate to a steering control technology.
2. Description of the Prior Art
When a driver steers a steering device while a vehicle travels, a tire may curvedly travel while slipping on the ground.
The center line of the tire and the traveling direction of the tire become different from each other according to such slipping. Further, a tire ground contact surface may increase in one direction. The one direction refers to a direction different from the traveling direction of the tire with reference to the center line of the tire.
A self-aligning torque, which tends to restore the tire to an original form in the center of the tire, is generated by the tire ground contact surface which has increased in one direction.
In other words, the driver should provide force against the self-aligning torque in order to steer the steering device.
Whereas, the self-aligning torque is dependent on a slip angle which is an angle formed by the center line of a tire and the traveling direction of the tire.
However, the self-aligning torque tends to increase in proportion to the slip angle up to a particular slip angle, but decrease at a slip angle above the particular slip angle.
Owing to such a tendency, when a driver provides force against the self-aligning torque to steer a steering device and thereby the slip angle of a vehicle exceeds the particular slip angle, the driver may unintentionally oversteer the steering device.